FAECAL PELLETS FROM MARINE DEPOSITS 25 



The estimates of the numbers of pellets per cubic centimetre, given in the table, 

 must be taken as only very rough approximations. The volumes of mud on which they 

 are based are the volumes of a portion of the deposit, shaken up in distilled water, and 

 allowed to settle for 24 hours at about 15'^ C. The highest number of the Nucula type of 

 pellet found was 79 per cc, which is about three times the highest value found in the 

 Clyde (Moore, 193 1, p. 355); but the highest value for the ovoid type — 179 per cc. — is 

 far lower than the value of 3400 per cc, from Loch Striven. 



The facts known with regard to the formation of these oval pellets may be summarized 

 as follows. They are of world-wide distribution, occurring in recent deposits in depths 

 of from o to over 4000 m., and in conditions varying from almost fresh to salt water, and 

 also in certain fossil deposits. Although more than one type is found (and E. M. Thorp 

 [personal communication] states that there are two common and easily distinguished 

 forms in the West Indian region), yet there is a simple oval type which occurs abundantly 

 in a number of localities. In structure they are composed of the same material as the 

 mud in which they are found, although naturally limited to the smaller particles of that 

 mud. They show no trace of concentric structure as would be expected if they were 

 oolite-like aggregates. Further, their occurrence as central cores for some oolites 

 suggests an entirely different origin from that of the outer layers of the oolites. The 

 possibility of their production by the roUing together of the surface layers of the mud 

 under the influence of currents is negatived by their comparative firmness, and also by 

 the fact that they may form as much as 100 per cent of the mud, with no interstitial fine 

 material at all. It is hard to see how such rolling could proceed so far as to remove the 

 whole of the fine material. It might, however, produce such a deposit composed en- 

 tirely of pellets by washing out all the fine material from between the heavier pellets. 

 Such a process would not account though for the presence in the mud of patches, such 

 as were occasionally found in the Clyde, where the whole of the mud had been converted 

 into pellets, these patches being quite small in extent, and sometimes surrounding the 

 mouth of the burrow of a worm (Moore, 1931, p. 354, fig. n). In relation to the latter 

 observation it is interesting to note that Galliher also (1931, p- 265) states that the fossil 

 "sporbo" occurs "in lenses parallel with the bedding and in small oval pockets". 



In favour of the animal origin of these pellets is the fact that the pellets from the 

 different localities appear to be similar, and that those from the Clyde have been defi- 

 nitely shown to be of animal origin, and that Maldanid worms, which are abundant in 

 these Clyde muds, shed a pellet identical in nature with the pellets found in the mud. 



Although the pellets of a number of littoral and shallow- water animals are now known, 

 nothing is as yet known of the pellets of any very deep-water animals (except for one or 

 two Anomura). The nature of the ovoid pellets suggests that they are those of either 

 polychaetes or molluscs ; they are not likely to be crustacean in origin (see Moore, 1932, 

 for general description of crustacean pellets). It remains, therefore, to obtain specimens 

 of the fauna of the muds in which these pellets are most abundant, and to examine 

 their gut contents to see whether similar pellets can be found in them. 



